The present invention relates to a motor controller and an electric power steering apparatus.
Conventionally, a power steering apparatus for a vehicle includes an electric power steering apparatus (EPS) provided with a motor as a drive source. The EPS has a lot of flexibility in the arrangement and an energy consumption is small in comparison with a hydraulic power steering apparatus. Accordingly, in recent years, the use of the EPS in many kinds of vehicles has been studied.
A motor has inherently has a fluctuation of an output torque, such as a cogging torque, a torque ripple caused by a distortion of an induced voltage waveform generated in a motor coil or the like. However, in the EPS, the fluctuation of the output torque mentioned above is reflected directly in a steering feeling. Accordingly, in the motor controller for the EPS, a lot of torque ripple countermeasures have been conventionally proposed.
For example, Japanese Laid-Open Patent Publication No. 2004-328814 discloses a motor controller generating a motor control signal on the basis of a current feedback control of a d/q coordinate system. This motor controller uses each of correction coefficients relating to a d-axis and a q-axis per an rotation angle of the motor computed on the basis of an actually measured data of the induced voltage waveform at a time of rotating the motor at a constant speed. Further, a d-axis current command value and a q-axis current command value are corrected by adding a d-axis correction amount and a q-axis correction amount corresponding to the rotation angle and computed on the basis of each of the correction coefficients to a d-axis current command value and a q-axis current command value corresponding to a target value of the current feedback control.
In other words, if a value of the induced voltage generated in each of phases due to the rotation of the motor per unit rotation angular velocity is known in each of the rotation angles (electric angles), it is possible to suppress the fluctuation of the output torque even in the case where the distortion is generated in the induced voltage waveform. That is, it is possible to determine a current value of each of the phases that does not generate any torque ripples.
For example, if the induced voltage value per unit rotation angular velocity (a unit induced voltage value) is set as in an expression (1) shown below, it is possible to determine, in accordance with the following expressions (2) to (4), the current value of each of the phases for preventing the torque ripple from being generated due to the distortion of the induced voltage waveform under a constraint condition in which a heat generation of the motor becomes minimum.
Expression
                                          e                          0              ⁢              u                                =                                    e              u                                      ω              m                                      ,                              e                          0              ⁢              v                                =                                    e              v                                      ω              m                                      ,                              e                          0              ⁢              w                                =                                    e              w                                      ω              m                                                          (        1        )                                          I          u                =                                                            (                                                      e                                          0                      ⁢                      u                                                        -                                      e                                          0                      ⁢                      v                                                                      )                            +                              (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      w                                                                      )                                                                                      (                                                            e                                              0                        ⁢                        u                                                              -                                          e                                              0                        ⁢                        v                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        v                                                              -                                          e                                              0                        ⁢                        w                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        w                                                              -                                          e                                              0                        ⁢                        u                                                                              )                                2                                              ⁢          T                                    (        2        )                                          I          v                =                                                            (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      w                                                                      )                            +                              (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      u                                                                      )                                                                                      (                                                            e                                              0                        ⁢                        u                                                              -                                          e                                              0                        ⁢                        v                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        v                                                              -                                          e                                              0                        ⁢                        w                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        w                                                              -                                          e                                              0                        ⁢                        u                                                                              )                                2                                              ⁢          T                                    (        3        )                                          I          w                =                                                            (                                                      e                                          0                      ⁢                      w                                                        -                                      e                                          0                      ⁢                      u                                                                      )                            +                              (                                                      e                                          0                      ⁢                      w                                                        -                                      e                                          0                      ⁢                      v                                                                      )                                                                                      (                                                            e                                              0                        ⁢                        u                                                              -                                          e                                              0                        ⁢                        v                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        v                                                              -                                          e                                              0                        ⁢                        w                                                                              )                                2                            +                                                (                                                            e                                              0                        ⁢                        w                                                              -                                          e                                              0                        ⁢                        u                                                                              )                                2                                              ⁢          T                                    (        4        )            
in which e0u, e0v, e0w represent unit induced voltage values for each phase, eu, ev, ew represent induced voltage waveforms for each phase (induced voltage values), ωm represents rotation angular velocities (mechanical angles), Iu, Iv, Iw represent current values for each phase, and T represents motor torque.
Accordingly, in the structure for carrying out the current feedback control of the d/q coordinate system, the d-axis current command value and the q-axis current command value may be computed by mapping (d/q conversion) the expressions (2) to (4) into the d/q coordinate.
Specifically, the expressions (2) to (4) are first transformed to the following expressions (5) to (7) and (8) to (10).
Expression
                              I          u                =                                            A              u                        ⁡                          (              θ              )                                ⁢                      K            t                    ⁢                      I            q            *                                              (        5        )                                          I          v                =                                            A              v                        ⁡                          (              θ              )                                ⁢                      K            t                    ⁢                      I            q            *                                              (        6        )                                          I          w                =                                            A              w                        ⁡                          (              θ              )                                ⁢                      K            t                    ⁢                      I            q            *                                              (        7        )                                                      A            u                    ⁡                      (            θ            )                          =                                            (                                                e                                      0                    ⁢                    u                                                  -                                  e                                      0                    ⁢                    v                                                              )                        +                          (                                                e                                      0                    ⁢                    v                                                  -                                  e                                      0                    ⁢                    w                                                              )                                                                          (                                                      e                                          0                      ⁢                      u                                                        -                                      e                                          0                      ⁢                      v                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      w                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      w                                                        -                                      e                                          0                      ⁢                      u                                                                      )                            2                                                          (        8        )                                                      A            v                    ⁡                      (            θ            )                          =                                            (                                                e                                      0                    ⁢                    v                                                  -                                  e                                      0                    ⁢                    w                                                              )                        +                          (                                                e                                      0                    ⁢                    v                                                  -                                  e                                      0                    ⁢                    u                                                              )                                                                          (                                                      e                                          0                      ⁢                      u                                                        -                                      e                                          0                      ⁢                      v                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      w                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      w                                                        -                                      e                                          0                      ⁢                      u                                                                      )                            2                                                          (        9        )                                                      A            w                    ⁡                      (            θ            )                          =                                            (                                                e                                      0                    ⁢                    w                                                  -                                  e                                      0                    ⁢                    u                                                              )                        +                          (                                                e                                      0                    ⁢                    w                                                  -                                  e                                      0                    ⁢                    v                                                              )                                                                          (                                                      e                                          0                      ⁢                      u                                                        -                                      e                                          0                      ⁢                      v                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      v                                                        -                                      e                                          0                      ⁢                      w                                                                      )                            2                        +                                          (                                                      e                                          0                      ⁢                      w                                                        -                                      e                                          0                      ⁢                      u                                                                      )                            2                                                          (        10        )            
in which, θ represents rotation angle (electric angle, Kt represents torque constant, and Iq* represents q-axis current command value.
Further, by d/q converting the expressions (5) to (7), it is possible to obtain the following expressions (11) and (12) as arithmetic expressions of a d-axis current command value Id0 and a q-axis current command value Iq0 for preventing torque ripple from being generated due to distortion of the induced voltage waveform.
Expression
                              I                      d            ⁢                                                  ⁢            0                          =                                            2              3                                ⁢                      {                                                                                A                    u                                    ⁡                                      (                    θ                    )                                                  ⁢                cos                ⁢                                                                  ⁢                θ                            +                                                                    A                    v                                    ⁡                                      (                    θ                    )                                                  ⁢                                  cos                  ⁡                                      (                                          θ                      -                                                                        2                          3                                                ⁢                        π                                                              )                                                              +                                                                    A                    w                                    ⁡                                      (                    θ                    )                                                  ⁢                                  cos                  ⁡                                      (                                          θ                      +                                                                        2                          3                                                ⁢                        π                                                              )                                                                        }                    ⁢                      K            t                    ⁢                      I            q            *                                              (        11        )                                          I                      q            ⁢                                                  ⁢            0                          =                                            2              3                                ⁢                      {                                                                                A                    u                                    ⁡                                      (                    θ                    )                                                  ⁢                sin                ⁢                                                                  ⁢                θ                            +                                                                    A                    v                                    ⁡                                      (                    θ                    )                                                  ⁢                                  sin                  ⁡                                      (                                          θ                      -                                                                        2                          3                                                ⁢                        π                                                              )                                                              +                                                                    A                    w                                    ⁡                                      (                    θ                    )                                                  ⁢                                  sin                  ⁡                                      (                                          θ                      +                                                                        2                          3                                                ⁢                        π                                                              )                                                                        }                    ⁢                      K            t                    ⁢                      I            q            *                                              (        12        )            
in which the expressions (11) and (12) can be further transformed into the following expressions (13) and (14), and (15) and (16).
Expression
                                              ⁢                              I                          d              ⁢                                                          ⁢              0                                =                                                    B                d                            ⁡                              (                θ                )                                      ×                          I              q                                                          (        13        )                                                          ⁢                              I                          q              ⁢                                                          ⁢              0                                =                                                                      B                  q                                ⁡                                  (                  θ                  )                                            ×                              I                q                *                                      +                          I              q              *                                                          (        14        )                                                      B            d                    ⁡                      (            θ            )                          =                                            2              3                                ⁢                      K            t                    ⁢                      {                                                                                A                    u                                    ⁡                                      (                    θ                    )                                                  ⁢                cos                ⁢                                                                  ⁢                θ                            +                                                                    A                    v                                    ⁡                                      (                    θ                    )                                                  ⁢                                  cos                  ⁡                                      (                                          θ                      -                                                                        2                          3                                                ⁢                        π                                                              )                                                              +                                                                    A                    w                                    ⁡                                      (                    θ                    )                                                  ⁢                                  cos                  ⁡                                      (                                          θ                      +                                                                        2                          3                                                ⁢                        π                                                              )                                                                        }                                              (        15        )                                                      B            q                    ⁡                      (            θ            )                          =                              -            1                    -                                                    2                3                                      ⁢                          K              t                        ⁢                          {                                                                                          A                      u                                        ⁡                                          (                      θ                      )                                                        ⁢                  sin                  ⁢                                                                          ⁢                  θ                                +                                                                            A                      v                                        ⁡                                          (                      θ                      )                                                        ⁢                                      sin                    ⁡                                          (                                              θ                        -                                                                              2                            3                                                    ⁢                          π                                                                    )                                                                      +                                                                            A                      w                                        ⁡                                          (                      θ                      )                                                        ⁢                                      sin                    ⁡                                          (                                              θ                        +                                                                              2                            3                                                    ⁢                          π                                                                    )                                                                                  }                                                          (        16        )            
In other words, on the assumption that a d-axis noninteracting control is executed (Id*=0), the d-axis current command value Id0 and the q-axis current command value Iq0 can be determined by respectively adding the corresponding d-axis correction amount (εd=Bd(θ)×Iq*) and the q-axis correction amount (εq=Bq(θ)×Iq*) to an original d-axis current command value Id* (Id*=0) and an original q-axis current command value Iq*.
Practically, first, the induced voltage values per unit rotation angular velocity for each rotation angle, that is, the unit induced voltage values e0u, e0v, and e0w are determined by measuring induced voltage waveforms (eu, ev, ew) of the respective phases at a time of rotating the motor at a constant speed, and dividing the measured value by the rotation angular velocity ωm (the mechanical angular velocity) at a time of rotating at the constant speed (refer to the expression (1)). Next, a map in which the rotation angle θ is associated with each of a d-axis correction coefficient Bd(θ) and a q-axis correction coefficient Bq(θ) is formed by computing the d-axis correction coefficient Bd(θ) and the q-axis correction coefficient Bq(θ) for each rotation angle θ on the basis of each of the unit induced voltage values e0u, e0v, and e0w, and the expressions (8) to (10), (15) and (16).
At the time of controlling the motor, the d-axis correction amount εd and the q-axis correction amount εq corresponding to the rotation angle θ are computed by referring to a map which is previously prepared and stored in a memory area (ROM), and the d-axis correction amount εd and the q-axis correction amount εq are added to the original d-axis current command value Id* and q-axis current command value Iq*. Further, it is possible to suppress the generation of torque ripple caused by distortion of the induced voltage waveform by executing the electric feedback control on the basis of the corrected d-axis current command value Id0 and q-axis current command value Iq0.
In the EPS, there is a case where the rotation of the motor is demanded in a high-speed region over a base speed at a time when a quick steering operation is generated or the like. As a method of ensuring a following capability at a time of steering at a high speed, there is a field weakening control setting the d-axis current command value to a negative value in correspondence to the rotation angular velocity of the motor. In other words, a magnetic flux in a direction of the d-axis in which a magnetic flux of a permanent magnet exists, is reduced by utilizing a demagnetizing electromotive force caused by a d-axis armature reaction generated by applying the d-axis current in the negative direction. Accordingly, an operating region of the motor is enlarged to a high-speed region over the base speed.
However, since the apparatus according to the prior art is structured on the assumption that the d-axis noninteracting control is executed (Id*=0), the prior art apparatus cannot correspond to the field weakening control mentioned above. In other words, the phase of each of the phase currents is deviated from the original phase through the execution of the field weakening control. Accordingly, it is impossible to properly correct the d-axis and q-axis current command values at a time of the field weakening control, and the generation of torque ripple is unavoidable.